Skip account selection if the invoice is already linked to an account

When the invoice is already linked to an account
And logged in user is part of the account, skip the account selection and take the user to payment method selection page. If the invoice is already paid, take the user to payment success page.
If the user is not part of the account linked to the invoice, show an error message.

The issue names no files or tests; start by locating the invoice account-selection flow and the routes for payment-method selection and payment success. Check how the linked account and current user are validated, then verify the three outcomes: skip selection for an eligible user, show success for a paid invoice, and show an error for an ineligible user.

Written by the indexing model from the issue text.